Projection system



Nov. 19, 1940. H. KUDAR PROJECTION SYSTEM Filed Feb. 15, 1937 Inventar 170 76 K n Attorneys Patented Nov. 19, 1940 UNITED STATES PROJECTION SYSTEM Hans Kudar, Berlin-Schoneberg, Germany, assignor to Telelunken Gesellschai't iiir Drahtlose Telegraphic m. b. IL, Berlin, Germany, a corporation of Germany In Germany February 13, 1936 Application February 15, 1937, Serial No. 125,856

6 Claims.

My .invention relates to a method of and means for clearly showing luminous pictures, more particularly television images upon fluorescent screens and cinematographic pictures upon a 5 projection screen, in illuminated rooms.

It is well known that for clearly showing projected or fluorescent pictures the room has to be darkened so as to avoid an undesirable illumina tion of the picture screen. I

According to the invention projected or fluorescent pictures of any kind can be clearly shown in illuminated rooms without any substantial undesirable illumination of the picture Screen by using artificial light having a narrow spectral range for lighting the room, and using a picture screen made out of a material adapted to absorb the spectrum of the room illumination, or protecting the picture screen from the effect of the room illumination by a filter pane consisting of such a material and arranged in front of thepicture screen. The light sources for lighting the room may emit one or more substantially monochromatic radiations and the absorbing medium contained in the picture screen or in the filter arranged in front of it should be opaque substantially only within the spectral range or ranges of the light sources. It has been found that it is particularly advantageous to use sodium vapor lamps for the room illumination, and neodymium as absorbing medium for protecting the picture screen against illumination by the light of said light sources. The sodium vapor lamp emanates practically monochromatic yellow light of a wave length between 570 and 600 and a translucent material like glass containing neodymium absorbs this very wave-length while it permits all other wave-lengths of the visible spectrum to penetrate through it almost undiminished. If a fluorescent screen is used of a kind producing comparatively white light, or substantially white light is used for projecting a picture, then, in an arrangement of this invention, the said white light is transmitted with the exception of the yellow D-line, and the result is a perfectly natural reproduction of the fluorescent or projected picture.

If the requirements regarding the room illumination are severer, then another single-wave may be added to the one before mentioned, with the result that the first radiation is so supplemented that the ensuing light will be as agreeable and pleasing as possible to the eye, For instance, what may be added to the yellow sodium vapor r light is a red or a bluish light, and also the latter should be practically single-wave in nature.

Anteriorly of the television receiver screen on the projection screen there should then be mounted another filter in addition to the neodymium filter in or in front of the screen, the said second filter being adapted to absorb the 5 second mentioned light.

The filter may be mounted at any convenient point between the television picture and the eye. For instance, the bulb of the cathode-ray-tube of a television receiver of the cathode-ray type, or at least the screen wall of the tube, may be made of the filter glass. Another embodiment consists in that the protective pane mounted anteriorly of the cathode-ray tube and which is to protect the eyes of the filter in case of accidental breaking of the tube, is made of filter glass; for instance, the safety glass marketed under the. trade-name of Sekurit and consisting of several glass sheets could have incorporated in it a certain addition of neodymium, or, for a room an illumination consisting of two monochromatic radiations, each one of the glass sheets of such glass may contain an absorbing medium adapted to absorb one of the radiations forming part of the room illumination.

A projection screen to be used for projecting pictures according to the invention may consist of a frosted mirror plate made of glass containing neodymium or .didymium.

In the drawing two embodiments of the inven- 30 tion are shown diagrammatically by way of example:

Fig. 1 shows an arrangement for showing television pictures,

Fig. 2 illustrates the use of the invention for showing cinematographic pictures.

The source of illumination l is a sodium-vapor lamp. In its stead could also be used a luminous source giving off light comprising several wavelengths, while in front thereof would then be fitted a filter designed to transmit only singlewave light. The television tube 2 is mounted posteriorly of a protective pane 3 which is fitted into the casing 4 of the television receiver. The said pane 3 serves two different purposes at the same time:' (1) it safeguards the viewer from scattered glass chips in case of accidental bursting of the television tube, and (2) the pane is of such a composition that it will permit nearly all wave-lengths inside the visible spectrum to penetrate and pass with the exception of the light of luminous source I. The said pane 3 consists preferably of neodymlferous glass. Another plan would be to mount a so-called Sekurit glass (safety) pane adjacent or in juxtaposition with a neodymiferous glass pane. Even if a fluorescent screen is employed which transmits a very wide spectrum including also the d line, the pane I, because of the low percentage of (1 line light in the entire spectral range of the fluorescent light will occasion a hardly appreciable attenuation of the luminosity of the teleyision image.

There is no absolute need for the pane I being built into the casing l, in fact, it could be mounted at some suitable place between the fluorescent screen and the viewer. Even if the light issued from source I should be able to directly strike the fluorescent screen 2 of the tube 2, the arrangement will be eflicient provided that the pane I is mounted somewhere in front of the viewer's eye.

The present invention is not conflned to the viewing of television images. For instance, in lieu of the fluorescent screen of tube 2 there could be used also a ground glass (matted) pane upon which a picture is projected. Because of the fact that pane l is mounted, this image would be visible from the illuminated room containing the onlookers just as is true of a cathode-ray tube. It would also be possible to dispose a wall at relatively great distance posteriorly of the pane 3, upon which wall a picture could be projected from the side of pane 3. In face, the projector could be arranged anteriorly of the pane 3 provided the cone of light is made to laterally skirt the said pane. In this manner motion-picture projection would be feasible even in brightly lit rooms or auditoriums.

The television receiver shown in the drawing may be of the type described in U. S. Patent No. 1,975,056 to W. L. Carlson, issued September 25, 1934.

In Fig. 2 the light source I is again a sodium- I vapor lamp while the light source 5 is a high pressure mercury vapor lamp emanating in first line blue light of a wave length of 436 a The projector 8 has a light source emitting substantially white light. The projection screen 1 consists of a frosted mirror plate made of glass containing neodymium, and in front of this screen there is an ordinary yellow filter 8 for protecting the screen from being illuminated by the blue light of the mercury vapor lamp 5. The screen 1 1 and the filter 8 are mounted in the frame 9.

What I claim is:

1. The method of showing luminous pictures in an illuminated room, which comprises illuminating the room with light of a predetermined narrow band of frequencies, projecting a picture in light of diiferent frequencies from that of the light illuminating the room on a viewing surface normally illuminated by said light of narrow band of frequencies within the room, and absorbing substantially only the light predetermined narrow bands of frequencies, projecting a picture in light of different frequencies from that of the light illuminating the room on a viewing surface normally illuminated by said light of narrow bands of frequencies within the room, and absorbing substantially only the light of said predetermined frequencies which is directly in register with the viewing surface to provide pictures of maximum contrast and undiminished intensity for an observer.

3. A device for showing luminous pictures in illuminated rooms, comprising a picture screen for producing luminous pictures within a room, means for lighting the room and said screen by light having a narrowspectral range and different from the spectral range of the luminous pictures, and an absorbing medium positioned adjacent to the picture screen and intermediate the lighting means and the picture screen and also positioned between said screen and an observer, said absorbing medium absorbing light substantially only in the same region as the narrow spectral range of the lighting means, whereby pictures of maximum contrast are viewed by the observer..

4. A device for showing television images upon a fluorescent screen in an illuminated room, comprising a television receiver wherein is provided a cathode ray tube having a fluorescent screen upon which images of predetermined spectral emission are produced, means for lighting the room and said tube by light having a narrow spectral emission range difierent from the spectral emission of the fluorescent screen, and means for absorbing only light substantially within the spectral range of the lighting means, said absorbing means being positioned adjacent to the fluorescent screen and intermediate the fluorescent screen and lighting means and located between said screen and an observer, whereby produced images of maximum contrast are viewed by said observer.

5. A device for showing projected cinamatographic pictures in illuminated rooms compris ing a projection screen, means for projecting pictures in light of wide spectral range upon the projection screen, means for lighting the room and said screen by light having a narrow spectral range, and an absorbing medium positioned adjacent to the projection screen and intermediate the projection screen and light means and also positioned between said screen and an observer, said absorbing medium absorbing light substantially only the same as the spectral range of the lighting means whereby the projected pictures of maximum contrast and undiminished intensity are viewed by said observer.

6. In combination, a picture viewing area within a room, a sodium vapor lamp illuminating said room and said viewing area, and a sheet of neodymium glass positioned adjacent to the viewing area and intermediate the viewing area and the sodium lamp, said sheet being between said viewing area and an observer, whereby pictures of maximum contrast are viewed by said observer.

HANS KUDAR. 

